N-alkylaminoalkyl(meth)acrylates are widely used as raw materials of polymer flocculating agents, lubricating additives, paper strength additives and the like. Above all, when manufacturing a polymer flocculating agent, in some cases, it has to be made to have a high molecular weight to improve its performance, and then there is a problem that a water insoluble gel material is formed. The mechanism of the formation of this gel material has not been fully understood, however, low boiling components contained in an N-alkylaminoalkyl (meth)acrylate, especially (meth)acrylic acid esters and N-alkylaminoalkyl alcohols that are reaction raw materials, are presumed to be a cause of it, and N-alkylaminoalkyl(meth)acrylates containing a small amount of these low boiling components are highly demanded. For example, a concentration of low boiling components contained in an N-alkylaminoalkyl(meth)acrylate is preferably not greater than 0.06 wt %, more preferably not greater than 0.05 wt %, and still more preferably not greater than 0.04 wt %, though it differs depending on a purpose of use and cannot be absolutely said.
Therefore, as a method of producing an N-alkylaminoalkyl (meth)acrylate, the following method is known, wherein an transesterification between a (meth)acrylic acid ester and an N-alkylaminoalkyl alcohol is performed in the presence of a catalyst, then, unreacted raw materials are distilled out from the reaction solution by distillation, and then, distillation of the target product N-alkylaminoalkyl(meth)acrylate is performed. However, there exist by-products of so-called Michael addition reaction (hereinafter referred to as Michael adducts) in the reaction solution formed by an addition reaction of the raw N-alkylaminoalkyl alcohol or a by-product alkyl alcohol to the double bonds of the raw (meth)acrylic acid ester or the target product N-alkylaminoalkyl (meth)acrylate. This Michael addition reaction is a reversible reaction and a decomposing reaction of the Michael adducts takes place not only during the transesterification but also during the following stages of distilling out the raw materials and distilling the target product, therefore, there is a problem that low boiling components such as the raw materials mix with the target product N-alkylaminoalkyl(meth)acrylate. To cope with this problem, various measures have been taken.
As a method of producing an N-alkylaminoalkyl(meth)acrylate containing a small amount of low boiling components, Patent document 1 and Patent document 2 disclose a method of producing a high purity N-alkylaminoalkyl(meth)acrylate, separating a catalyst from a reaction solution in advance to distilling out the low boiling components and refining a target product in a stage of refining after performing an transesterification in a presence of a catalyst.
Further, Patent document 3 and Patent document 4 disclose a method of reducing low boiling components in an N-alkylaminoalkyl(meth)acrylate by pyrolysis treatment of by-products.
In addition, Patent document 5 discloses a method of suppressing side reactions by adding the raw N-alkylaminoalkyl alcohol to the reaction system with a passage of time.
Patent document 1: Japanese Patent Application Laid-Open No. 11-322680.
Patent document 2: Japanese Patent Application Laid-Open No. 3-112949.
Patent document 3: Japanese Patent Application Laid-Open No. 11-222469.
Patent document 4: Japanese Patent Application Laid-Open No. 10-279540.
Patent document 5: Japanese Patent Application Laid-Open No. 4-95054.
Patent document 6: Japanese Patent Application Laid-Open No. 8-268938.